The present invention relates in general to an apparatus for testing microelectronic elements, and more particularly, to an interposer for testing microelectronic elements in the nature of bare printed circuits having a plurality of contacts arranged in matrices having normal and high contact pitch densities.
Electrical testing of microelectronic elements such as circuit elements and printed circuit boards, is typically conducted using drilled plates including dielectric materials. The drilled openings serve to guide spring loaded probes of the test fixture to test point locations which are of interest on the printed circuit. The probes may be either "hard" or permanently wired or they may be removable as is the case in systems where the text fixture is placed on a standard base grid of programmable test points.
FIG. 1 shows a printed circuit board 1 having a standard grid of test points 2 whereby all of the test probes 3 of the text fixture 4 are in alignment therewith. The system commonly uses "pogo pins" in a "bed-of-nails" configuration as shown. This system has reliably served the testing needs of the printed circuit industry for many years, however, at present there is a need to advance the state of the art to address two important issues: 1) the increasing density of test points associated with newer surface mount components, and 2) the need to translate grid points from a nominal 0.100" to grid pitches which may be either metric based or English based, often on the same circuit. It is the express purpose of this invention to address these needs by providing a low cost system for electrically testing local high contact pitch density areas of a printed circuit board. The system should be able to simultaneously test both high contact pitch density areas and normal contact pitch density areas on a circuit board.
FIG. 2 shows one system presently being used to test the high density areas of a printed circuit board. As is evident from FIG. 2, these fixtures are considerably complex. In order to contact the test points located in high density areas, some of the test probes 5 are angled toward one another so that the tops of the probes are closer together. However, this test system has additional cost in terms of both electronic and mechanical elements, and most of the test points will be unused most of the time.
Accordingly, there is an unsolved need for a test fixture which can accommodate microelectronic elements such as printed circuits and the like having contacts disposed thereon, for example, in both high contact pitch density and normal contact pitch density.